Building a narrow entry bench with storage from plywood and basic tools

Our entryway is narrow, and I want a slim bench where we can sit to put on shoes and hide a couple of baskets underneath. Plywood seems easier than solid wood with my basic tools: circular saw, drill and clamps. The bench can't be too deep or we'll clip our knees passing through. I'm sketching a simple box with internal supports rather than a complicated frame. How would you prevent wobble without turning it into a bulky cabinet?